When a two-piece can in which a can body and a can bottom are integrated, for example, a drawn-ironed can or stretched-drawn-ironed can (in the present description, when the two types of cans are not distinguished from each other, both will be referred to as drawn-ironed can) is molded, the so-called ironing process is performed in which the desired shape is molded, while inserting the can material into a narrow gap between a punch and a die. In such ironing processing, the can material is literally covered on the punch and the can material is strongly pressed against and ironed by a die called an ironing die. As a result, the can material is stretched over the punch and it is difficult to separate the punch and the can material (poor stripping ability). Therefore, a variety of stripper devices that overcome such poor removability of the can material have been suggested. These devices are composed of a plurality of fingers that come into contact with the opening end portion of the can material and the outer circumferential surface of the punch. These fingers have hooks at the distant ends thereof and are tightly arranged annularly along the end portion of a sleeve, while being biased in the direction of closing the hooks located at the distant ends of the fingers by an annular spring (elastic body). The can material that has been stretched over the punch upon completion of the ironing process is firstly passed through the sleeve of the stripper device. In this case, the can material is directed toward a doming process, which is a very last processing step, while pushing out and spreading the fingers. Because the fingers are thus percussively spread by the can material, the can material is dented, and when the fingers are then percussively closed causing a jumping phenomenon, the can material is further dented. Alternatively, the can material is scratched and dented by finger hooks. In a punch return process, the edge portion of the can body (can material) and the distal end engagement portion of the fingers are engaged and the can is removed from the punch. A force that closes the fingers depends on the biasing force of the annular elastic body.
In order to prevent the can body from being dented by the fingers, a stripper device has been suggested in which opening and closing of the fingers biased by an annular spring in the closing direction is controlled by an outer cam ring that cannot move in the axial direction, but is capable of moving in the circumferential direction, and an inner cam ring that is capable of moving in the axial direction (see, for example, Patent Document 1). In this stripper device, in the forward stroke of the punch, where the outer cam ring is forcibly rotated by a lever, the inner cam moves axially to an upper dead center, thereby opening the fingers and allowing the can body engaged with the punch to pass, and in the return stroke of the punch, the outer cam ring rotates in the opposite direction and returns to the original state, whereby the fingers are closed by the annular spring, the distal end of the can is engaged with the fingers, and the can body is separated from the punch. With such a configuration, the vicinity of the distal end of the punch is prevented from hitting the fingers and the can body is not dented. However, in some cases the fingers interfere with each other and all the fingers are not closed completely. The resultant problem is that the can may be cracked in the axial direction in the vicinity of those fingers that have not been closed.
In order to resolve this problem, a stripper device has been suggested (see, for example, Patent Document 2) in which the length of the engagement portions at the distal end of each finger is increased to ensure that the fingers do not interfere, the fingers are installed independently and annularly in six segments along a center hole, each finger is provided with a rocking fulcrum and biased by a spring in the closing direction, and a cam follower is installed in the head portion of each finger. In addition, an outer cam ring is rotatably supported and the outer cam ring is rotated by a lever so that when the cam follower mates with a concave portion (recess) of the outer cam ring, the finger swings (rotates) in the direction of closing by the action of the spring, whereas when the cam follower abuts against a flat portion (not receding portion) of the outer cam ring, the finger swings in the direction of opening against the spring force. As a result, each finger is forcibly and independently opened and closed.
Patent Document 1: Japanese Examined Patent Publication No. H6-59509.
Patent Document 2: Japanese Patent No. 3858651.